The present invention is related in general to the acoustic monitoring of pipelines and vessels which carry pressurized gas or liquid, and in particular to a new and useful method and apparatus of monitoring pressurized vessels for small leaks, explosions or hard hits.
U.S. Pat. No. 5,416,724, which is incorporated here by reference, was issued May 16, 1995 to the inventor of the present application. That patent disclosed a technique for detecting leaks in pressurized pipelines or vessels, using an acoustic sensor and in conjunction with a specific technique of analysis for analyzing the signals from the acoustic sensor to identify the presence of a leak.
Fast, reliable detection of large or small leaks of gaseous and liquid materials from storage and pipeline facilities is an important problem. If the material is explosive, even small holes in high pressure gas pipelines can quickly result in the formation of dangerous, large gas clouds. also if an underground or above ground vessel is struck by a hard object or a power tool, it might be damaged. In a situation like this it is necessary to determine the location of the impact and send a crew to inspect the vessel for possible damage.
Some definitions and assumptions used in this disclosure:
1. In this disclosure the word "vessel" is used to describe a container filled with a gas or liquid under high or low pressure, including containers and pipelines.
2. It is presumed that the vessel may have any shape, such as the shape of a barrel, the shape of a pipeline or other shape.
3. The term "rupture" is used to describe a sudden breach or explosion of the wall of a vessel under pressure, resulting in a large leak.
4. The vessel may be located above ground, underground or submerged in a liquid.
5. Concerning an "acoustic signal", all vessels under pressure have two important characteristics. These characteristics are a) the mechanical resonance of the vessel, and b) the propagation of mechanical waves through the vessel.
a) If a vessel is mechanically excited such as if it is struck by a hard object, the vessel will oscillate (resonate) for a while at it's mechanical resonant frequency. The resonant characteristic includes the amplitude, frequency and the damping factor and it is determined by the dimensions and by the material of which the vessel is made.
If at least one dimension of the vessel is large, it takes time for a sound wave to propagate from one point of the vessel to another, and propagation characteristics of the sound through the vessel must be considered. Since vessels come in many different shapes, a model used in this disclosure will contain both the resonant and the propagation characteristics, and this model will be the pipeline. In other words in this disclosure the pipeline is used to be a representative of all vessels.
Some existing continuous leak detection systems rely on methods such as volume balance comparison [1] while others rely on detection of the leaking fluid [2]. These systems, however, can only detect relatively large leaks and may allow a potentially dangerous situation to develop quickly without detection [3]. FNT [1] W. C. Thompson and K. D. Skogman. "The Application of Real Time Flow Modeling to Pipeline Leak Detection" in K. Chickering, editor, Pipeline Engineering Symposium, pp. 39-45. the American Society of Mechanical Engineers, 1983. FNT [2] C. Sandbert et al. "The Application of a Continuous Leak Detection System to Pipelines and Associated Equipment," IEEE Transactions on Industry Applications, pp. 906-909, September, October 1989. FNT [3] S. Olafson, "An Alarm in Tulsa, Then Time Ran Out in Brenham," The Houston Post, pg. A1, nday, Apr. 12, 1992.